School Database

[xionhack]

Hello. I am trying to make a web application for something that works as a school. The points are:

 

The students can become teachers later on. There are only 20 subjects that the teacher should teach. I want to record, which of those subjects can the teacher teach, and for the students, which subjects have they studied, with who, and which other subjects they have to study.

 

I am new at object oriented programming, so I was trying to do it with classes so I could learn more, but I think Im not doing it correctly. Can somebody explain to me which approach should I take? Thanks!

[br0ken]

That's a pretty vague question but here goes...

 

You need to create a class for each entity. I was always taught you should have a class for each noun (this is only mostly true). For example, you would need a Teacher class and a Student Class. You would Also need a Lesson class.

 

Hopefully this will help but if not, try and be more specific with your question.

[xionhack]

I have a question about that. A student, can be a teacher, So i was thinking about making only one table with boths infos, do i still have to make 2 classes

[ignace]

A student, can be a teacher

 

You'll have to think this through very carefully. IMO should you create a separate table for both teacher and student because a student is not a teacher although data may be in some circumstances similar (name, birthdate) between both, a student does not have an employment record (in normal circumstances) nor does the teacher get graded. In OOP terms it also does not make any sense as:

 

a student is-a teacher OR a teacher is-a student

 

class Student extends Teacher {}
class Teacher extends Student {}

 

In the first scenario is a student capable of more then the teacher while in the other you would have an overhead (getGrades(), getTimesFlunked(), ..) functions that make no sense in a Teacher context.

 

In OOP it is a good practice to use Value Objects (or Active Records)

 

class Student {}
class Teacher {}

 

Consider for example:

 

public function setGrades(Teacher $t, Student $s, array $grades)

 

Now assume you said a Student is-a Teacher which assumes this is equally true:

 

public function setGrades(Student $t, Student $s, array $grades)

 

And to prevent this from happening you would always have to write:

 

if ($t instanceof Teacher)

[br0ken]

Ignace is correct that a Student and Teacher are separate entities and therefore both need a separate class, but you are also right in noticing they share a common factor; they are both a human!

 

The best way to do this would be to have a base class Human (or Person) and have both Teacher and Student extend from them.

 

<?php

abstract class Human {

protected $_name = '';
protected $_gender = '';
protected $_role = '';

public function getName()
{
  return $this->_name;
}

}


class Teacher extends Human {

public function __construct($name)
{
  $this->_name = $name;
  $this->_role = 'Teacher';
  }
}

class Student extends Human {

public function __construct($name)
{
  $this->_name = $name;
  $this->_role = 'Student';
  }
}

$teacher = new Teacher('Mrs Smith');
$student = new Student('Jack Adams');

echo $teacher->getName(); //Returns Mrs Smith
echo $student->getName(); // Returns Jack Adams

?>

 

The benefit of this method is that both Teacher and Student can use the Human functions. This will save you duplicating code between the two objects.